A problem faced by aquarists who rely on traditional undergravel filters in the bottoms of their aquariums is that the gravel traps and accumulates fecal and vegetable matter, algae, unconsumed food, and various other kinds of detritus. The only way to clean this type of filter is to break down the entire aquarium by uprooting the filter, disconnecting all electrical leads and air tubes, and removing the entire contents of the aquarium, including all fish, plants, ornaments, etc. This is labor-intensive and time-consuming, not to mention the time, effort and skill required to restore the aquarium to its original condition with a completely new water charge having a balanced pH and ideal temperature.
Removing fish from their "home" for cleaning in this manner is very stressful and is a cause for loss in many cases, especially where proper procedures are not followed because of lack of knowledge on the part of the hobbyist, or taking shortcuts to save time or effort.